Designs

[jander14indoor]

Not sure what you mean by "geometric" angle of attack, but the ideal angle of attack for any flying surface depends on many things and there is no one ideal angle. For this event you want your surfaces to be flying at the best lift over drag point for the speed they fly in mid-flight. This tends to be very near stall on these planes.

Jeff Anderson
Livonia, MI

[Taran]

And also, Is it necessary to have stab tips, or should you just use a single rudder?

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Wright Stuff
Meteorology
Can't Judge a Powder

[jcollier]

Either design will work. Ziegler Freedom Flights kit have a single rudder. Cezar Banks Leading Edge uses tip plates. Both can fly well enough to win just about any competition if they are trimmed well and you have good flight data.

[calgoddard]

"I just read a book about flight and it said that a good geometric angle of attack is around 13 degrees, but seeing all the planes people have built, they are nowhere near 13 degrees. May be only for heavy aircraft?"

This will follow up Jeff Anderson's answer to the above question.

Some experts are of the opinion that indoor duration rubber powered airplanes should not have any downthrust, i.e. the axis of the propeller shaft should be parallel to the longitudinal axis of the motor stick and the rubber motor.

Then the airplane needs decalage, a fancy French word for saying that the stab should have a negative incidence of about one degree and the main wing should have a positive incidence of about one to two degrees, and maybe three degrees at most.

Typically one fixes the incidence of the stab for simplicity and the raises and lowers the leading edge of the main wing by sliding the forward main wing post up and down.

Keep raising the leading edge of the main wing until you detect a slight stall, i.e. an up and down pitching of the front end of the airplane. Then lower the leading edge until the stall just disappears.

Warning: with the very large chord of the main wing of the 2010 WS airplanes that do not seek the bonus it is much harder to detect a stall than with narrower main wing chords.

[emd19]

We have two days before states and we need a good quality plane design that can be built quickly. It doesn't have to be insane, as long as it flies more than 45 seconds.
Thanks

[Taran]

Probably something that looks like a Leading Edge or Freedom Flight would work.

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Wright Stuff (State: )
Meteorology (State: 1st)
Can't Judge A Powder (State 1st)

[wlsguy]

I received an email fro A2Z aka Peck Polymers for a snow sale (it snowed in Denver this week) with a note that you could download for free the Leading Edge plans. The link is

http://www.a2zcorp.us/freedownload/Lead ... nePlan.pdf

You may note on the plans the caveat about the tip plates consistent with Jander's warning to me--the plates must be glued on at exactly 90 degrees.

A common design is available above.
Yes, I can be built rather quickly (2~3 hours) if you have the materials

I will say that 2 days before the State Competition is very late to be building.
Unless you have time to practice, don't expect great results. (and don't blame the design because it is one of the better ones out there)

[jander14indoor]

2-3 hours build needs a lot of experience building these models as well as materials to complete a Leading Edge design.

OK, if goal is 45 seconds, take that design and SIMPLIFY.
Select fairly light balsa, say 7-8 lb/ft3.
Reduce wing size to 10 cm chord. Use 3/32 by 1/16 inch sticks on edge for spars. Same for ribs, don''t worry about curve. Don't use fins, crack the spars and kick up the outer 10 cm of each tip by 3 cm or so. Glue cracked spars to lock in dihedral. Cover with light tissue or light plastic grocery bags.
Glue a 1/8 by 1/4 hard balsa stick along the chord 1 cm to right of center line so it sticks out beyond wing about 1 cm. Glue a 1/8 inch riser under the leading edge. Make sure the wing is flat or left leading edge is twisted higher than right a little. NOT the right leading edge higher than left.

Tail, build a flat rectangle 5 cm longer than the max span the rules allow by say 5-6 cm chord. Again, build it flat, but with 1/16 inch square. Cover same as wing. Crack the spars and kick up the outer 2.6 cm of both tips by 90 degrees.

Motor stick, 10 inchs long by 1/4 by 3/8 light balsa. Tail boom 8-12 inches 1/4 by 1/8 tapering to 1/8 by 1/8. Offset tip of tailboom to centerline of motorstick about 1/2 inch to the left. Add tail hook and prop hanger, reinforce with thread wrapping coated by glue.

Glue the rear stab on with a 1/16 inch riser under the rear spar. Make sure it tilts to the right so left tip is 1/2 or so higher than right.

Attach wing to motor stick with dental bands front and back. Slide wing to balance with prop, motor, everything at about the rear spar to start.

Test glide with a couple hundred winds in a 3/32 1.5 gm motor. It should fly level with a slight descent. If stalling move wing back. If diving, move wing forward or raise leading edge by wedging a piece of wood under the attachment stick at front. Add winds to start climbing. WIND it. Lube your motors.

If you are under 10 grams and trim it right, such a plane can hit 45 seconds. With two days, your goal should be to finish your plane and trim it well enough to fly at least level in a 30 foot diameter circle. Any more is gravy in that short time, unless you have a mentor on hand.

Oh, and spend some time reading the 800 or so messages in this forum.

Good luck

Jeff Anderson
Livonia, MI

[calgoddard]

Cezar Banks' 2010 WS airplane is a very good design. Built correctly, trimmed properly, and with the proper rubber and winds, it can win Nationals.

That being said, I have a fair amount of experience and it would take me 8 - 12 hours to build Cezar's 2010 WS airplane correctly, and then at least that much time to trim it properly and figure out the best prop, rubber, winds, etc. for the expected flight venue.

With only two days time available, Jeff Anderson has given you good advice given the fact that your goal is a 45 second flight.

[blue cobra]

Would anyone be interested in seeing a picture of my plane? I'm just wondering, since I don't find it that impressive, but it's not the Leading Edge, so that alone kind of makes it unique this year